1. Field of the Invention
This invention relates to rotary cone rock bits and the manipulation of the hydraulic energy exiting the fluid jet nozzles retained within the rock bit as the bit works in an earthen formation borehole.
More particularly, this invention relates to the use of one or more diffuser type nozzles in the outer periphery of a rotary cone rock bit body thereby providing improved cross flow by increasing bulk fluid motion across the borehole bottom. The use of diffuser nozzles also provides additional cone cleaning without eroding the cones as well as allowing for detritous removal past the diffuser jets positioned near the gage of the bit as the bit works in a borehole.
Diffuser type nozzles normally are used only in the center or dome portion of rotary cone bits to remove debris that accumulates or "balls" in the space above the cones centrally of the bit when the bit is in operation. The use of diffuser jets on gage of rotary cone bits is especially affective in the softer, sticky types of earthen formations.
2. Background
The use of nozzle jets in rotary cone rock bits to clean the cutting surfaces of the cones and to sweep the borehole clean of detritous as the rock bit is advanced in a borehole is well known in the petroleum industry.
Normally, a three cone rock bit consists of a center diffusion jet and three high flow/high velocity jets adjacent each 120 degree leg segment of the bit body and positioned near the peripheral edge or gage of the bit.
The center jet is a relatively low velocity diverging jet nozzle that widely diffuses fluid to keep the cutter cones clean and to remove debris that tends to ball up between the cones. The high velocity jets adjacent the gage of the bit direct fluid toward the borehole bottom to clear rock chips from the borehole so that the cutter cones may advance into the formation without grinding up old cuttings. Unfortunately, if the high velocity fluid of these jets passes to close to the cone surface, excessive cone erosion may occur resulting in lost inserts and damage to the cutter cones.
U.S. Pat. Nos. 4,369,849 and 4,516,642 attempt to direct fluid flow in such a manner as to move detritous from the borehole bottom. The '849 patent utilizes multiple nozzles at various angles with respect to the axis of the rock bit. The nozzles are also positioned around the dome area in a spiral pattern. The spiral nozzle configuration attempts to create a spiral flow path of fluid on the borehole bottom.
The '642 patent teaches directing a stream of fluid through a nozzle at the leading cutting edge of a rotary cutter cone to both clean the cutting elements of the cone and to move formation cuttings away from the advancing roller cone. In a multiple cone bit, each cone has its own fluid nozzle. The nozzle is canted or angled toward the leading edge of the rotary cone to clean the cone cutters extending from the surface of the cone. Unfortunately, the cuttings tend to circulate on bottom due to the nozzles being circumferentially spaced around the rock bit body.
U.S. Pat. Nos. 4,126,194; 4,187,921 and 4,189,014 are assigned to the same assignee as the present invention and are hereby incorporated by reference. These patents generally teach sweeping the bottom of a formation to remove debri therefrom.
The '194 patent teaches the use of two nozzles, one each in 120 degree leg segments, the third 120 degree leg segment having a funnel type pickup tube axially aligned with the rock bit body. An inlet end of the pickup tube is positioned just above the borehole bottom. The object of the pickup tube is to sweep formation cuttings across the bottom and up the pickup tube. While this concept has considerable merit, the pickup tube lacks sufficient size to handle a large volume of cuttings,
The '921 patent utilizes opposed extended nozzles in a two rotary cone rock bit. Crossflow of hydraulic fluid is generated by cavitating one of the two opposed nozzles. The pressure differential between the pair of nozzles encourages crossflow thereby sweeping the borehole bottom during rock bit operation.
The '014 patent was also designed to enhance crossflow of drilling fluid over a borehole bottom. Two nozzles, one each in 120 degree leg segments are mounted in the bit body so that they extend slightly from a dome portion of the bit. Each nozzle is sealed on the gage side of the 120 degree leg segment to assure crossflow of fluid toward the remaining nozzleless 120 degree leg segment. The nozzleless segment is open to the borehole annulus for passage of the detritous up the annulus to the rig floor. A flow diverter is mounted in the center of the dome to decrease the dome area thereby increasing the flow velocity around the diverter and across the bit face. The diverter also serves to discourage the accumulation of formation cuttings that tend to accumulate or "ball up" in the center of the bit adjacent the dome.
If the detritous is not efficiently removed, the rock bit regrinds the cuttings endlessly resulting in shortening the life of the rock bit and a lessened bit penetration rate.
U.S. Pat. No. 5,293,946 teaches and claims a divergent type fluid nozzle for one piece drag rock bits. The nozzles are designed to take advantage of the Coanda effect whereby the fluid adheres to the diverging nozzle wall downstream of the throat section of the nozzle thereby minimizing turbulent flow exiting the nozzles. By opening up the nozzle exit, the patentee's teach that the nozzle is less apt to clog. Clogging of the fluid nozzles is a distinct possibility of drag type rock bits since the nozzle is necessarily positioned in the cutting face of the drag bit immediately adjacent the borehole bottom.
The present invention primarily uses diffusion type nozzles around the outer peripheral edge of the rock bit to clean the cones and to enhance cross flow of fluid across the hole bottom to increase the rate of penetration on the bit in a borehole.